package regression

import (
	"context"
	"crypto/md5"
	"errors"
	"fmt"
	"math"
	"sync"
	"time"

	"go.skia.org/infra/go/skerr"
	"go.skia.org/infra/go/sklog"
	"go.skia.org/infra/go/vcsinfo"
	"go.skia.org/infra/go/vec32"
	"go.skia.org/infra/perf/go/alerts"
	"go.skia.org/infra/perf/go/cid"
	"go.skia.org/infra/perf/go/clustering2"
	"go.skia.org/infra/perf/go/config"
	"go.skia.org/infra/perf/go/dataframe"
	"go.skia.org/infra/perf/go/shortcut"
	"go.skia.org/infra/perf/go/types"
)

// ProcessState is the state of a RegressionDetectionProcess.
type ProcessState string

const (
	PROCESS_RUNNING ProcessState = "Running"
	PROCESS_SUCCESS ProcessState = "Success"
	PROCESS_ERROR   ProcessState = "Error"
)

const (
	// MAX_FINISHED_PROCESS_AGE is the amount of time to keep a finished
	// RegressionDetectionRequestProcess around before deleting it.
	MAX_FINISHED_PROCESS_AGE = time.Minute

	// The following limits are just to prevent excessively large or long-running
	// regression detections from being triggered.

	// MAX_K is the largest K used for clustering.
	MAX_K = 100

	// MAX_RADIUS  is the maximum number of points on either side of a commit
	// that will be included in regression detection.
	MAX_RADIUS = 50

	// SPARSE_BLOCK_SEARCH_MULT When searching for commits that have data in a
	// sparse data set, we'll request data in chunks of this many commits per
	// point we are looking for.
	SPARSE_BLOCK_SEARCH_MULT = 2000
)

var (
	errorNotFound = errors.New("Process not found.")
)

// RegressionDetectionRequest is all the info needed to start a clustering run,
// an Alert and the Domain over which to run that Alert.
type RegressionDetectionRequest struct {
	Alert  *alerts.Alert `json:"alert"`
	Domain types.Domain  `json:"domain"`
}

// Id returns a unique identifier for the request.
func (c *RegressionDetectionRequest) Id() string {
	return fmt.Sprintf("%x", md5.Sum([]byte(fmt.Sprintf("%#v", *c))))
}

// RegressionDetectionResponse is the response from running a RegressionDetectionRequest.
type RegressionDetectionResponse struct {
	Summary *clustering2.ClusterSummaries `json:"summary"`
	Frame   *dataframe.FrameResponse      `json:"frame"`
}

// RegressionDetectionProcess handles the processing of a single RegressionDetectionRequest.
type RegressionDetectionProcess struct {
	// These members are read-only, should not be modified.
	request           *RegressionDetectionRequest
	vcs               vcsinfo.VCS
	iter              DataFrameIterator
	responseProcessor RegressionDetectionResponseProcessor
	shortcutStore     shortcut.Store
	ctx               context.Context

	// mutex protects access to the remaining struct members.
	mutex      sync.RWMutex
	response   []*RegressionDetectionResponse // The response when the detection is complete.
	lastUpdate time.Time                      // The last time this process was updated.
	state      ProcessState                   // The current state of the process.
	message    string                         // Describes the current state of the process.
}

func newProcess(ctx context.Context, req *RegressionDetectionRequest, vcs vcsinfo.VCS, cidl *cid.CommitIDLookup, dfBuilder dataframe.DataFrameBuilder, shortcutStore shortcut.Store, responseProcessor RegressionDetectionResponseProcessor) (*RegressionDetectionProcess, error) {
	ret := &RegressionDetectionProcess{
		request:           req,
		vcs:               vcs,
		responseProcessor: responseProcessor,
		response:          []*RegressionDetectionResponse{},
		lastUpdate:        time.Now(),
		state:             PROCESS_RUNNING,
		message:           "Running",
		shortcutStore:     shortcutStore,
		ctx:               ctx,
	}
	// Create a single large dataframe then chop it into 2*radius+1 length sub-dataframes in the iterator.
	iter, err := NewDataFrameIterator(ctx, ret.progress, req, dfBuilder, vcs)
	if err != nil {
		return nil, fmt.Errorf("Failed to create iterator: %s", err)
	}
	ret.iter = iter
	return ret, nil
}

func newRunningProcess(ctx context.Context, req *RegressionDetectionRequest, vcs vcsinfo.VCS, cidl *cid.CommitIDLookup, dfBuilder dataframe.DataFrameBuilder, shortcutStore shortcut.Store, responseProcessor RegressionDetectionResponseProcessor) (*RegressionDetectionProcess, error) {
	ret, err := newProcess(ctx, req, vcs, cidl, dfBuilder, shortcutStore, responseProcessor)
	if err != nil {
		return nil, err
	}
	go ret.Run()
	return ret, nil
}

// RunningRegressionDetectionRequests keeps track of all the RegressionDetectionProcess's.
//
// Once a RegressionDetectionProcess is complete the results will be kept in memory
// for MAX_FINISHED_PROCESS_AGE before being deleted.
type RunningRegressionDetectionRequests struct {
	vcs                vcsinfo.VCS
	cidl               *cid.CommitIDLookup
	defaultInteresting float32 // The threshold to control if a regression is considered interesting.
	dfBuilder          dataframe.DataFrameBuilder
	shortcutStore      shortcut.Store

	mutex sync.Mutex
	// inProcess maps a RegressionDetectionRequest.Id() of the request to the RegressionDetectionProcess
	// handling that request.
	inProcess map[string]*RegressionDetectionProcess
}

// NewRunningRegressionDetectionRequests return a new RegressionDetectionRequests.
func NewRunningRegressionDetectionRequests(vcs vcsinfo.VCS, cidl *cid.CommitIDLookup, interesting float32, dfBuilder dataframe.DataFrameBuilder, shortcutStore shortcut.Store) *RunningRegressionDetectionRequests {
	fr := &RunningRegressionDetectionRequests{
		vcs:                vcs,
		cidl:               cidl,
		inProcess:          map[string]*RegressionDetectionProcess{},
		defaultInteresting: interesting,
		dfBuilder:          dfBuilder,
		shortcutStore:      shortcutStore,
	}
	go fr.background()
	return fr
}

// step does a single step in cleaning up old RegressionDetectionProcess's.
func (fr *RunningRegressionDetectionRequests) step() {
	fr.mutex.Lock()
	defer fr.mutex.Unlock()
	now := time.Now()
	for k, v := range fr.inProcess {
		v.mutex.Lock()
		if now.Sub(v.lastUpdate) > MAX_FINISHED_PROCESS_AGE {
			delete(fr.inProcess, k)
		}
		v.mutex.Unlock()
	}
}

// background periodically cleans up old RegressionDetectionProcess's.
func (fr *RunningRegressionDetectionRequests) background() {
	fr.step()
	for range time.Tick(time.Minute) {
		fr.step()
	}
}

// Add starts a new running RegressionDetectionProcess and returns
// the ID of the process to be used in calls to Status() and
// Response().
func (fr *RunningRegressionDetectionRequests) Add(ctx context.Context, req *RegressionDetectionRequest) (string, error) {
	fr.mutex.Lock()
	defer fr.mutex.Unlock()
	if req.Alert.Interesting == 0 {
		req.Alert.Interesting = fr.defaultInteresting
	}
	id := req.Id()
	if p, ok := fr.inProcess[id]; ok {
		state, _, _ := p.Status()
		if state != PROCESS_RUNNING {
			delete(fr.inProcess, id)
		}
	}
	responseProcessor := func(_ *RegressionDetectionRequest, _ []*RegressionDetectionResponse) {}
	if _, ok := fr.inProcess[id]; !ok {
		proc, err := newRunningProcess(ctx, req, fr.vcs, fr.cidl, fr.dfBuilder, fr.shortcutStore, responseProcessor)
		if err != nil {
			return "", err
		}
		fr.inProcess[id] = proc
	}
	return id, nil
}

// Status returns the ProcessingState and the message of a
// RegressionDetectionProcess of the given 'id'.
func (fr *RunningRegressionDetectionRequests) Status(id string) (ProcessState, string, error) {
	fr.mutex.Lock()
	defer fr.mutex.Unlock()
	p, ok := fr.inProcess[id]
	if !ok {
		return PROCESS_ERROR, "Not Found", errorNotFound
	}
	return p.Status()
}

// Response returns the RegressionDetectionResponse of the completed RegressionDetectionProcess.
func (fr *RunningRegressionDetectionRequests) Response(id string) (*RegressionDetectionResponse, error) {
	fr.mutex.Lock()
	defer fr.mutex.Unlock()
	p, ok := fr.inProcess[id]
	if !ok {
		return nil, errorNotFound
	}
	return p.Response(), nil
}

// Responses returns the RegressionDetectionResponse's of the completed RegressionDetectionProcess.
func (fr *RunningRegressionDetectionRequests) Responses(id string) ([]*RegressionDetectionResponse, error) {
	fr.mutex.Lock()
	defer fr.mutex.Unlock()
	p, ok := fr.inProcess[id]
	if !ok {
		return nil, errorNotFound
	}
	return p.Responses(), nil
}

// reportError records the reason a RegressionDetectionProcess failed.
func (p *RegressionDetectionProcess) reportError(err error, message string) {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	sklog.Warningf("RegressionDetectionRequest failed: %#v %s: %s", *(p.request), message, err)
	p.message = fmt.Sprintf("%s: %s", message, err)
	p.state = PROCESS_ERROR
	p.lastUpdate = time.Now()
}

// progress records the progress of a RegressionDetectionProcess.
func (p *RegressionDetectionProcess) progress(step, totalSteps int) {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	p.message = fmt.Sprintf("Querying: %d%%", int(float32(100.0)*float32(step)/float32(totalSteps)))
	p.lastUpdate = time.Now()
}

// detectionProgress records the progress of a RegressionDetectionProcess.
func (p *RegressionDetectionProcess) detectionProgress(totalError float64) {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	p.message = fmt.Sprintf("Regression Total Error: %0.2f", totalError)
	p.lastUpdate = time.Now()
}

// Response returns the RegressionDetectionResponse of the completed RegressionDetectionProcess.
func (p *RegressionDetectionProcess) Response() *RegressionDetectionResponse {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	return p.response[0]
}

// Responses returns all the RegressionDetectionResponse's of the RegressionDetectionProcess.
func (p *RegressionDetectionProcess) Responses() []*RegressionDetectionResponse {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	return p.response
}

// Status returns the ProcessingState and the message of a
// RegressionDetectionProcess of the given 'id'.
func (p *RegressionDetectionProcess) Status() (ProcessState, string, error) {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	return p.state, p.message, nil
}

// missing returns true if >50% of the trace is vec32.MISSING_DATA_SENTINEL.
func missing(tr types.Trace) bool {
	count := 0
	for _, x := range tr {
		if x == vec32.MISSING_DATA_SENTINEL {
			count++
		}
	}
	return (100*count)/len(tr) > 50
}

// tooMuchMissingData returns true if a trace has too many
// MISSING_DATA_SENTINEL values.
//
// The criteria is if there is >50% missing data on either side of the target
// commit, which sits at the center of the trace.
func tooMuchMissingData(tr types.Trace) bool {
	if len(tr) < 3 {
		return false
	}
	n := len(tr) / 2
	if tr[n] == vec32.MISSING_DATA_SENTINEL {
		return true
	}
	return missing(tr[:n]) || missing(tr[len(tr)-n:])
}

// ShortcutFromKeys stores a new shortcut for each regression based on its Keys.
func (p *RegressionDetectionProcess) ShortcutFromKeys(summary *clustering2.ClusterSummaries) error {
	var err error
	for _, cs := range summary.Clusters {
		if cs.Shortcut, err = p.shortcutStore.InsertShortcut(context.Background(), &shortcut.Shortcut{Keys: cs.Keys}); err != nil {
			return err
		}
	}
	return nil
}

// Run does the work in a RegressionDetectionProcess. It does not return until all the
// work is done or the request failed. Should be run as a Go routine.
func (p *RegressionDetectionProcess) Run() {
	if p.request.Alert.Algo == "" {
		p.request.Alert.Algo = types.KMEANS_GROUPING
	}
	for p.iter.Next() {
		df, err := p.iter.Value(p.ctx)
		if err != nil {
			p.reportError(err, "Failed to get DataFrame from DataFrameIterator.")
			return
		}
		sklog.Infof("Next dataframe: %d traces", len(df.TraceSet))
		before := len(df.TraceSet)
		// Filter out Traces with insufficient data. I.e. we need 50% or more data
		// on either side of the target commit.
		df.FilterOut(tooMuchMissingData)
		after := len(df.TraceSet)
		sklog.Infof("Filtered Traces: %d %d %d", before, after, before-after)

		k := p.request.Alert.K
		if k <= 0 || k > MAX_K {
			n := len(df.TraceSet)
			// We want K to be around 50 when n = 30000, which has been determined via
			// trial and error to be a good value for the Perf data we are working in. We
			// want K to decrease from  there as n gets smaller, but don't want K to go
			// below 10, so we use a simple linear relation:
			//
			//  k = 40/30000 * n + 10
			//
			k = int(math.Floor((40.0/30000.0)*float64(n) + 10))
		}
		sklog.Infof("Clustering with K=%d", k)

		var summary *clustering2.ClusterSummaries
		switch p.request.Alert.Algo {
		case types.KMEANS_GROUPING:
			summary, err = clustering2.CalculateClusterSummaries(df, k, config.MinStdDev, p.detectionProgress, p.request.Alert.Interesting, p.request.Alert.Step)
		case types.STEPFIT_GROUPING:
			summary, err = StepFit(df, k, config.MinStdDev, p.detectionProgress, p.request.Alert.Interesting, p.request.Alert.Step)

		default:
			p.reportError(skerr.Fmt("Invalid type of clustering: %s", p.request.Alert.Algo), "Invalid type of clustering.")
		}
		if err != nil {
			p.reportError(err, "Invalid regression detection.")
			return
		}
		if err := p.ShortcutFromKeys(summary); err != nil {
			p.reportError(err, "Failed to write shortcut for keys.")
			return
		}

		df.TraceSet = types.TraceSet{}
		frame, err := dataframe.ResponseFromDataFrame(p.ctx, df, p.vcs, false)
		if err != nil {
			p.reportError(err, "Failed to convert DataFrame to FrameResponse.")
			return
		}

		p.mutex.Lock()
		p.state = PROCESS_SUCCESS
		p.message = ""
		cr := &RegressionDetectionResponse{
			Summary: summary,
			Frame:   frame,
		}
		p.responseProcessor(p.request, []*RegressionDetectionResponse{cr})
		p.response = append(p.response, cr)
		p.mutex.Unlock()
	}
}