// Copyright 2022 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

pub status "#bad header"
pub status "#bad run length encoding"
pub status "#unsupported TGA file"

pub const DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE : base.u64 = 0

pub struct decoder? implements base.image_decoder(
	width  : base.u32[..= 0xFFFF],
	height : base.u32[..= 0xFFFF],

	// Call sequence states:
	//  - 0x00: initial state.
	//  - 0x03: image config decoded.
	//  - 0x04: frame config decoded.
	//  - 0xFF: end-of-data, usually after (the non-animated) frame decoded.
	//
	// State transitions:
	//
	//  - 0x00 -> 0x03: via DIC
	//  - 0x00 -> 0x04: via DFC with implicit DIC
	//  - 0x00 -> 0xFF: via DF  with implicit DIC and DFC
	//
	//  - 0x03 -> 0x04: via DFC
	//  - 0x03 -> 0xFF: via DF  with implicit DFC
	//
	//  - 0x04 -> 0xFF: via DFC
	//  - 0x04 -> 0xFF: via DF
	//
	//  - ???? -> 0x03: via RF  for ???? > 0x00
	//
	// Where:
	//  - DF  is decode_frame
	//  - DFC is decode_frame_config, implicit means nullptr args.dst
	//  - DIC is decode_image_config, implicit means nullptr args.dst
	//  - RF  is restart_frame
	call_sequence : base.u8,

	header_id_length                   : base.u8,
	header_color_map_type              : base.u8,
	header_image_type                  : base.u8,
	header_color_map_first_entry_index : base.u16,
	header_color_map_length            : base.u16,
	header_color_map_entry_size        : base.u8,
	header_pixel_depth                 : base.u8,
	header_image_descriptor            : base.u8,

	opaque : base.bool,

	scratch_bytes_per_pixel : base.u32[..= 4],
	src_bytes_per_pixel     : base.u32[..= 4],
	src_pixfmt              : base.u32,

	frame_config_io_position : base.u64,

	swizzler : base.pixel_swizzler,
	util     : base.utility,
)(
	dst_palette : array[4 * 256] base.u8,
	src_palette : array[4 * 256] base.u8,
	scratch     : array[4] base.u8,
)

pub func decoder.set_quirk_enabled!(quirk: base.u32, enabled: base.bool) {
}

pub func decoder.decode_image_config?(dst: nptr base.image_config, src: base.io_reader) {
	var c  : base.u32
	var c5 : base.u32[..= 0x1F]
	var i  : base.u32

	if this.call_sequence <> 0 {
		return base."#bad call sequence"
	}

	this.header_id_length = args.src.read_u8?()
	this.header_color_map_type = args.src.read_u8?()
	if this.header_color_map_type > 1 {
		return "#bad header"
	}

	this.header_image_type = args.src.read_u8?()
	if (this.header_image_type == 0x01) or
		(this.header_image_type == 0x02) or
		(this.header_image_type == 0x03) or
		(this.header_image_type == 0x09) or
		(this.header_image_type == 0x0A) or
		(this.header_image_type == 0x0B) {
		// No-op.
	} else {
		// TODO: 0x20 and 0x21 are invalid, according to the spec, but are
		// apparently unofficial extensions.
		return "#bad header"
	}

	this.header_color_map_first_entry_index = args.src.read_u16le?()
	this.header_color_map_length = args.src.read_u16le?()
	this.header_color_map_entry_size = args.src.read_u8?()
	if this.header_color_map_type <> 0 {
		// We have a color-mapped image (in Wuffs, an indexed pixel format).
		if (this.header_color_map_first_entry_index <> 0) or
			(this.header_color_map_length > 0x100) {
			return "#unsupported TGA file"
		} else if (this.header_color_map_entry_size <> 0x0F) and
			(this.header_color_map_entry_size <> 0x10) and
			(this.header_color_map_entry_size <> 0x18) and
			(this.header_color_map_entry_size <> 0x20) {
			return "#bad header"
		}
	} else {
		// The color-map fields must be zero.
		if (this.header_color_map_first_entry_index <> 0) or
			(this.header_color_map_length <> 0) or
			(this.header_color_map_entry_size <> 0) {
			return "#bad header"
		}
	}

	// Ignore the X-Origin and Y-Origin fields.
	args.src.skip_u32?(n: 4)

	this.width = args.src.read_u16le_as_u32?()
	this.height = args.src.read_u16le_as_u32?()

	this.header_pixel_depth = args.src.read_u8?()
	if (this.header_pixel_depth <> 0x01) and
		(this.header_pixel_depth <> 0x08) and
		(this.header_pixel_depth <> 0x0F) and
		(this.header_pixel_depth <> 0x10) and
		(this.header_pixel_depth <> 0x18) and
		(this.header_pixel_depth <> 0x20) {
		return "#bad header"
	}

	if (this.header_image_type | 8) == 0x09 {
		this.scratch_bytes_per_pixel = 1
		this.src_bytes_per_pixel = 1
		this.src_pixfmt = base.PIXEL_FORMAT__INDEXED__BGRA_NONPREMUL
		this.opaque =
			(this.header_color_map_entry_size == 0x0F) or
			(this.header_color_map_entry_size == 0x18)

	} else if (this.header_image_type | 8) == 0x0A {
		if (this.header_pixel_depth == 0x0F) or
			(this.header_pixel_depth == 0x10) {
			// Wuffs' base.pixel_swizzler doesn't support BGRX5551, so
			// scratch_bytes_per_pixel and src_bytes_per_pixel are different.
			this.scratch_bytes_per_pixel = 4
			this.src_bytes_per_pixel = 0
			this.src_pixfmt = base.PIXEL_FORMAT__BGRA_NONPREMUL
		} else if this.header_pixel_depth == 0x18 {
			this.scratch_bytes_per_pixel = 3
			this.src_bytes_per_pixel = 3
			this.src_pixfmt = base.PIXEL_FORMAT__BGR
			this.opaque = true
		} else if this.header_pixel_depth == 0x20 {
			this.scratch_bytes_per_pixel = 4
			this.src_bytes_per_pixel = 4
			this.src_pixfmt = base.PIXEL_FORMAT__BGRA_NONPREMUL
		} else {
			return "#unsupported TGA file"
		}

	} else {
		if this.header_pixel_depth == 0x08 {
			this.scratch_bytes_per_pixel = 1
			this.src_bytes_per_pixel = 1
			this.src_pixfmt = base.PIXEL_FORMAT__Y
			this.opaque = true
		} else {
			return "#unsupported TGA file"
		}
	}

	this.header_image_descriptor = args.src.read_u8?()
	if (this.header_image_descriptor & 0x10) <> 0 {
		// We don't support right-to-left, only left-to-right pixel order.
		return "#unsupported TGA file"
	}

	// Skip the Image ID.
	args.src.skip_u32?(n: this.header_id_length as base.u32)

	// Read the color map.
	if this.header_color_map_type <> 0 {
		while i < (this.header_color_map_length as base.u32) {
			assert i <= 0xFFFF via "a <= b: a <= c; c <= b"(c: this.header_color_map_length as base.u32)
			if this.header_color_map_entry_size == 0x18 {
				c = args.src.read_u24le_as_u32?()
				this.src_palette[((i & 0xFF) * 4) + 0] = ((c >> 0x00) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 1] = ((c >> 0x08) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 2] = ((c >> 0x10) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 3] = 0xFF
			} else if this.header_color_map_entry_size == 0x20 {
				c = args.src.read_u32le?()
				this.src_palette[((i & 0xFF) * 4) + 0] = ((c >> 0x00) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 1] = ((c >> 0x08) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 2] = ((c >> 0x10) & 0xFF) as base.u8
				this.src_palette[((i & 0xFF) * 4) + 3] = ((c >> 0x18) & 0xFF) as base.u8
			} else {
				// Expand 15-bit or 16-bit color map entries.
				c = args.src.read_u16le_as_u32?()
				c5 = 0x1F & (c >> 0)
				this.src_palette[((i & 0xFF) * 4) + 0] = ((c5 << 3) | (c5 >> 2)) as base.u8
				c5 = 0x1F & (c >> 5)
				this.src_palette[((i & 0xFF) * 4) + 1] = ((c5 << 3) | (c5 >> 2)) as base.u8
				c5 = 0x1F & (c >> 10)
				this.src_palette[((i & 0xFF) * 4) + 2] = ((c5 << 3) | (c5 >> 2)) as base.u8
				// TODO: can the alpha value be zero (BGRA5551 not BGRX5551)?
				this.src_palette[((i & 0xFF) * 4) + 3] = 0xFF
			}
			i += 1
		} endwhile
		while i < 0x100 {
			this.src_palette[(i * 4) + 0] = 0x00
			this.src_palette[(i * 4) + 1] = 0x00
			this.src_palette[(i * 4) + 2] = 0x00
			this.src_palette[(i * 4) + 3] = 0xFF
			i += 1
		} endwhile
	}

	this.frame_config_io_position = args.src.position()

	if args.dst <> nullptr {
		args.dst.set!(
			pixfmt: this.src_pixfmt,
			pixsub: 0,
			width: this.width,
			height: this.height,
			first_frame_io_position: this.frame_config_io_position,
			first_frame_is_opaque: this.opaque)
	}

	this.call_sequence = 3
}

pub func decoder.decode_frame_config?(dst: nptr base.frame_config, src: base.io_reader) {
	if this.call_sequence < 3 {
		this.decode_image_config?(dst: nullptr, src: args.src)
	} else if this.call_sequence == 3 {
		if this.frame_config_io_position <> args.src.position() {
			return base."#bad restart"
		}
	} else if this.call_sequence == 4 {
		this.call_sequence = 0xFF
		return base."@end of data"
	} else {
		return base."@end of data"
	}

	if args.dst <> nullptr {
		args.dst.set!(bounds: this.util.make_rect_ie_u32(
			min_incl_x: 0,
			min_incl_y: 0,
			max_excl_x: this.width,
			max_excl_y: this.height),
			duration: 0,
			index: 0,
			io_position: this.frame_config_io_position,
			disposal: 0,
			opaque_within_bounds: this.opaque,
			overwrite_instead_of_blend: false,
			background_color: 0xFF00_0000)
	}

	this.call_sequence = 4
}

pub func decoder.decode_frame?(dst: ptr base.pixel_buffer, src: base.io_reader, blend: base.pixel_blend, workbuf: slice base.u8, opts: nptr base.decode_frame_options) {
	var status              : base.status
	var dst_pixfmt          : base.pixel_format
	var dst_bits_per_pixel  : base.u32[..= 256]
	var dst_bytes_per_pixel : base.u64[..= 32]
	var dst_x               : base.u32
	var dst_y               : base.u32
	var tab                 : table base.u8
	var dst_palette         : slice base.u8
	var dst                 : slice base.u8
	var dst_start           : base.u64
	var src_palette         : slice base.u8
	var mark                : base.u64
	var num_pixels64        : base.u64
	var num_pixels32        : base.u32[..= 0xFFFF]
	var lit_length          : base.u32[..= 0xFFFF]
	var run_length          : base.u32[..= 0xFFFF]
	var num_dst_bytes       : base.u64[..= 0x1F_FFE0]
	var num_src_bytes       : base.u32[..= 0x3_FFFC]
	var c                   : base.u32
	var c5                  : base.u32[..= 0x1F]

	if this.call_sequence < 4 {
		this.decode_frame_config?(dst: nullptr, src: args.src)
	} else if this.call_sequence == 4 {
		// No-op.
	} else {
		return base."@end of data"
	}

	if this.header_color_map_type <> 0 {
		src_palette = this.src_palette[..]
	}
	status = this.swizzler.prepare!(
		dst_pixfmt: args.dst.pixel_format(),
		dst_palette: args.dst.palette_or_else(fallback: this.dst_palette[..]),
		src_pixfmt: this.util.make_pixel_format(repr: this.src_pixfmt),
		src_palette: src_palette,
		blend: args.blend)
	if not status.is_ok() {
		return status
	}

	// TODO: the dst_pixfmt variable shouldn't be necessary. We should be able
	// to chain the two calls: "args.dst.pixel_format().bits_per_pixel()".
	dst_pixfmt = args.dst.pixel_format()
	dst_bits_per_pixel = dst_pixfmt.bits_per_pixel()
	if (dst_bits_per_pixel & 7) <> 0 {
		return base."#unsupported option"
	}
	dst_bytes_per_pixel = (dst_bits_per_pixel / 8) as base.u64

	if (this.header_image_descriptor & 0x20) == 0 {  // Bottom-to-top.
		dst_y = this.height ~mod- 1
	}
	if (this.header_image_type & 8) == 0 {
		// No RLE (run length encoding) means that the entire row is
		// effectively literals.
		lit_length = this.width
	}

	while.resume true {
		tab = args.dst.plane(p: 0)
		dst_palette = args.dst.palette_or_else(fallback: this.dst_palette[..])

		while dst_y < this.height {
			dst = tab.row_u32(y: dst_y)
			dst_start = (dst_x as base.u64) * dst_bytes_per_pixel
			if dst_start <= dst.length() {
				dst = dst[dst_start ..]
			} else {
				dst = this.util.empty_slice_u8()
			}

			while dst_x < this.width {
				assert dst_x <= 0xFFFF via "a <= b: a <= c; c <= b"(c: this.width)

				if this.src_bytes_per_pixel > 0 {
					if lit_length > 0 {
						mark = args.src.mark()
						num_pixels64 = args.src.length() / (this.src_bytes_per_pixel as base.u64)
						num_pixels32 = num_pixels64.min(a: lit_length as base.u64) as base.u32
						num_dst_bytes = (num_pixels32 as base.u64) * dst_bytes_per_pixel
						num_src_bytes = num_pixels32 * this.src_bytes_per_pixel
						args.src.skip_u32?(n: num_src_bytes)
						this.swizzler.swizzle_interleaved_from_slice!(
							dst: dst,
							dst_palette: dst_palette,
							src: args.src.since(mark: mark))
						if num_dst_bytes <= dst.length() {
							dst = dst[num_dst_bytes ..]
						} else {
							dst = this.util.empty_slice_u8()
						}
						dst_x += num_pixels32
						lit_length = (lit_length ~mod- num_pixels32) & 0xFFFF
						if lit_length > 0 {
							yield? base."$short read"
							continue.resume
						}

					} else if run_length > 0 {
						run_length -= 1
						this.swizzler.swizzle_interleaved_from_slice!(
							dst: dst,
							dst_palette: dst_palette,
							src: this.scratch[.. this.scratch_bytes_per_pixel])
						if dst_bytes_per_pixel <= dst.length() {
							dst = dst[dst_bytes_per_pixel ..]
						}
						dst_x += 1

					} else {
						// Handle Raw vs RLE packets.
						if args.src.length() <= 0 {
							yield? base."$short read"
							continue.resume
						}
						if args.src.peek_u8_as_u32() < 0x80 {
							lit_length = args.src.peek_u8_as_u32() + 1
							args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							if (lit_length + dst_x) > this.width {
								return "#bad run length encoding"
							}

						} else {
							if this.src_bytes_per_pixel == 1 {
								if args.src.length() < 2 {
									yield? base."$short read"
									continue.resume
								}
								run_length = (args.src.peek_u8_as_u32() & 0x7F) + 1
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[0] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							} else if this.src_bytes_per_pixel == 3 {
								if args.src.length() < 4 {
									yield? base."$short read"
									continue.resume
								}
								run_length = (args.src.peek_u8_as_u32() & 0x7F) + 1
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[0] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[1] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[2] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							} else {  // this.src_bytes_per_pixel == 4
								if args.src.length() < 5 {
									yield? base."$short read"
									continue.resume
								}
								run_length = (args.src.peek_u8_as_u32() & 0x7F) + 1
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[0] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[1] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[2] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
								this.scratch[3] = args.src.peek_u8()
								args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							}

							if (run_length + dst_x) > this.width {
								return "#bad run length encoding"
							}
						}
					}

				} else {
					// Wuffs' base.pixel_swizzler doesn't support BGRX5551, so
					// we manually convert to BGRX8888, one pixel at a time.

					if lit_length > 0 {
						if args.src.length() < 2 {
							yield? base."$short read"
							continue.resume
						}
						c = args.src.peek_u16le_as_u32()
						args.src.skip_u32_fast!(actual: 2, worst_case: 2)
						c5 = 0x1F & (c >> 0)
						this.scratch[0] = ((c5 << 3) | (c5 >> 2)) as base.u8
						c5 = 0x1F & (c >> 5)
						this.scratch[1] = ((c5 << 3) | (c5 >> 2)) as base.u8
						c5 = 0x1F & (c >> 10)
						this.scratch[2] = ((c5 << 3) | (c5 >> 2)) as base.u8
						// TODO: can the alpha value be zero (BGRA5551 not BGRX5551)?
						this.scratch[3] = 0xFF
						this.swizzler.swizzle_interleaved_from_slice!(
							dst: dst,
							dst_palette: dst_palette,
							src: this.scratch[.. 4])
						if dst_bytes_per_pixel <= dst.length() {
							dst = dst[dst_bytes_per_pixel ..]
						}
						dst_x += 1
						lit_length -= 1

					} else if run_length > 0 {
						run_length -= 1
						this.swizzler.swizzle_interleaved_from_slice!(
							dst: dst,
							dst_palette: dst_palette,
							src: this.scratch[.. this.scratch_bytes_per_pixel])
						if dst_bytes_per_pixel <= dst.length() {
							dst = dst[dst_bytes_per_pixel ..]
						}
						dst_x += 1

					} else {
						// Handle Raw vs RLE packets.
						if args.src.length() <= 0 {
							yield? base."$short read"
							continue.resume
						}
						if args.src.peek_u8_as_u32() < 0x80 {
							lit_length = args.src.peek_u8_as_u32() + 1
							args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							if (lit_length + dst_x) > this.width {
								return "#bad run length encoding"
							}

						} else {
							if args.src.length() < 3 {
								yield? base."$short read"
								continue.resume
							}
							run_length = (args.src.peek_u8_as_u32() & 0x7F) + 1
							args.src.skip_u32_fast!(actual: 1, worst_case: 1)
							c = args.src.peek_u16le_as_u32()
							args.src.skip_u32_fast!(actual: 2, worst_case: 2)
							c5 = 0x1F & (c >> 0)
							this.scratch[0] = ((c5 << 3) | (c5 >> 2)) as base.u8
							c5 = 0x1F & (c >> 5)
							this.scratch[1] = ((c5 << 3) | (c5 >> 2)) as base.u8
							c5 = 0x1F & (c >> 10)
							this.scratch[2] = ((c5 << 3) | (c5 >> 2)) as base.u8
							// TODO: can the alpha value be zero (BGRA5551 not BGRX5551)?
							this.scratch[3] = 0xFF

							if (run_length + dst_x) > this.width {
								return "#bad run length encoding"
							}
						}
					}
				}
			} endwhile
			dst_x = 0

			if (this.header_image_descriptor & 0x20) == 0 {  // Bottom-to-top.
				dst_y ~mod-= 1
			} else {  // Top-to-bottom.
				dst_y ~mod+= 1
			}
			if (this.header_image_type & 8) == 0 {
				// No RLE (run length encoding) means that the entire row is
				// effectively literals.
				lit_length = this.width
			}
		} endwhile
		break.resume
	} endwhile.resume

	this.call_sequence = 0xFF
}

pub func decoder.frame_dirty_rect() base.rect_ie_u32 {
	return this.util.make_rect_ie_u32(
		min_incl_x: 0,
		min_incl_y: 0,
		max_excl_x: this.width,
		max_excl_y: this.height)
}

pub func decoder.num_animation_loops() base.u32 {
	return 0
}

pub func decoder.num_decoded_frame_configs() base.u64 {
	if this.call_sequence > 3 {
		return 1
	}
	return 0
}

pub func decoder.num_decoded_frames() base.u64 {
	if this.call_sequence > 4 {
		return 1
	}
	return 0
}

pub func decoder.restart_frame!(index: base.u64, io_position: base.u64) base.status {
	if this.call_sequence < 3 {
		return base."#bad call sequence"
	}
	if args.index <> 0 {
		return base."#bad argument"
	}
	this.call_sequence = 3
	this.frame_config_io_position = args.io_position
	return ok
}

pub func decoder.set_report_metadata!(fourcc: base.u32, report: base.bool) {
	// TODO: implement.
}

pub func decoder.tell_me_more?(dst: base.io_writer, minfo: nptr base.more_information, src: base.io_reader) {
	return base."#no more information"
}

pub func decoder.workbuf_len() base.range_ii_u64 {
	return this.util.make_range_ii_u64(min_incl: 0, max_incl: 0)
}