// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package frontend

import (
	"fmt"
	"sort"
	"strings"

	"golang.org/x/pkgsite/internal"
)

// Symbol is an element in the package API. A symbol can be a constant,
// variable, function, type, field or method.
type Symbol struct {
	// Name is name of the symbol. At a given package version, name must be
	// unique.
	Name string

	// Synopsis is the one line description of the symbol that is displayed.
	Synopsis string

	// Section is the section that a symbol appears in.
	Section internal.SymbolSection

	// Kind is the type of a symbol, which is either a constant, variable,
	// function, type, field or method.
	Kind internal.SymbolKind

	// Link is the link to the symbol name on pkg.go.dev.
	Link string

	// Children contain the child symbols for this symbol. This will
	// only be populated when the SymbolType is "Type". For example, the
	// children of net/http.Handler are FileServer, NotFoundHandler,
	// RedirectHandler, StripPrefix, and TimeoutHandler. Each child
	// symbol will have ParentName set to the Name of this type.
	Children []*Symbol

	// Builds lists all of the build contexts supported by the symbol, it is
	// only available for limited set of builds. If the symbol supports all
	// build contexts, Builds will be nil.
	Builds []string

	// builds keeps track of build contexts used to generate Builds.
	builds map[internal.BuildContext]bool

	// New indicates that the symbol is new as of the version where it is
	// present. For example, if type Client was introduced in v1.0.0 and
	// Client.Timeout was introduced in v1.1.0, New will be false for Client
	// and true for Client.Timeout if this Symbol corresponds to v1.1.0.
	New bool
}

func (s *Symbol) addBuilds(builds []internal.BuildContext) {
	if s.builds == nil {
		s.builds = map[internal.BuildContext]bool{}
	}
	for _, b := range builds {
		s.builds[b] = true
	}
}

// symbolsForVersions returns an array of symbols for use in the VersionSummary
// of the specified version.
func symbolsForVersion(pkgURLPath string, symbolsAtVersion map[string]map[internal.SymbolMeta]*internal.UnitSymbol) [][]*Symbol {
	nameToMetaToSymbol := map[string]map[internal.SymbolMeta]*Symbol{}
	children := map[internal.SymbolMeta]*internal.UnitSymbol{}
	for _, smToUs := range symbolsAtVersion {
		for sm, us := range smToUs {
			if sm.ParentName != sm.Name {
				// For the children, keep track of them for later.
				children[sm] = us
				continue
			}

			metaToSym, ok := nameToMetaToSymbol[us.Name]
			if !ok {
				metaToSym = map[internal.SymbolMeta]*Symbol{}
				nameToMetaToSymbol[us.Name] = metaToSym
			}
			s, ok := metaToSym[sm]
			if !ok {
				s = &Symbol{
					Name:     sm.Name,
					Synopsis: sm.Synopsis,
					Section:  sm.Section,
					Kind:     sm.Kind,
					Link:     symbolLink(pkgURLPath, sm.Name, us.BuildContexts()),
					New:      true,
				}
				nameToMetaToSymbol[us.Name][sm] = s
			}
			s.addBuilds(us.BuildContexts())
		}
	}

	for cm, cus := range children {
		// Option 1: no parent exists
		// - make one, add to map
		// - append to parent
		// Option 2: parent exists and supports child bc
		// - append to parent
		// Option 3 parent exists and does not support child bc
		// - append to parent
		cs := &Symbol{
			Name:     cm.Name,
			Synopsis: cm.Synopsis,
			Section:  cm.Section,
			Kind:     cm.Kind,
			Link:     symbolLink(pkgURLPath, cm.Name, cus.BuildContexts()),
			New:      true,
		}

		parents, ok := nameToMetaToSymbol[cm.ParentName]
		var found bool
		if ok {
			for _, ps := range parents {
				for build := range ps.builds {
					if cus.SupportsBuild(build) {
						ps.Children = append(ps.Children, cs)
						found = true
						break
					}
				}
			}
		}
		if found {
			continue
		}

		// We did not find a parent, so create one.
		ps := createParent(cus, pkgURLPath)
		ps.Children = append(ps.Children, cs)
		pm := internal.SymbolMeta{
			Name:       ps.Name,
			ParentName: ps.Name,
			Synopsis:   ps.Synopsis,
			Section:    ps.Section,
			Kind:       ps.Kind,
		}
		ps.addBuilds(cus.BuildContexts())
		nameToMetaToSymbol[pm.Name] = map[internal.SymbolMeta]*Symbol{
			pm: ps,
		}
	}

	var symbols []*Symbol
	for _, mts := range nameToMetaToSymbol {
		for _, s := range mts {
			if len(s.builds) != len(internal.BuildContexts) {
				for b := range s.builds {
					s.Builds = append(s.Builds, fmt.Sprintf("%s/%s", b.GOOS, b.GOARCH))
				}
				sort.Strings(s.Builds)
			}
			symbols = append(symbols, s)
		}
	}
	return sortSymbols(symbols)
}

func symbolLink(pkgURLPath, name string, builds []internal.BuildContext) string {
	if len(builds) == len(internal.BuildContexts) {
		return fmt.Sprintf("%s#%s", pkgURLPath, name)
	}

	// When a symbol is introduced for a specific GOOS/GOARCH at a version,
	// linking to an unspecified GOOS/GOARCH page might not take the user to
	// the symbol. Instead, link to one of the supported build contexts.
	return fmt.Sprintf("%s?GOOS=%s#%s", pkgURLPath, builds[0].GOOS, name)
}

// createParent creates a parent symbol for the provided unit symbol. This is
// used when us is a child of a symbol that may have been introduced at a
// different version. The symbol created will have New set to false, since this
// function is only used when a parent symbol is not found for the unit symbol,
// which means it was not introduced at the same version.
func createParent(us *internal.UnitSymbol, pkgURLPath string) *Symbol {
	s := &Symbol{
		Name:     us.ParentName,
		Synopsis: fmt.Sprintf("type %s", us.ParentName),
		Section:  internal.SymbolSectionTypes,
		Kind:     internal.SymbolKindType,
		Link:     symbolLink(pkgURLPath, us.ParentName, us.BuildContexts()),
	}
	s.addBuilds(us.BuildContexts())
	return s
}

// sortSymbols returns an array of symbols in order of
// (1) Constants (2) Variables (3) Functions and (4) Types.
// Within each section, symbols are sorted alphabetically by name.
// In the types sections, aside from interfaces, child symbols are sorted in
// order of (1) Fields (2) Constants (3) Variables (4) Functions and (5)
// Methods. For interfaces, child symbols are sorted in order of
// (1) Methods (2) Constants (3) Variables and (4) Functions.
func sortSymbols(symbols []*Symbol) [][]*Symbol {
	sm := map[internal.SymbolSection][]*Symbol{}
	for _, parent := range symbols {
		sm[parent.Section] = append(sm[parent.Section], parent)
		cm := map[internal.SymbolKind][]*Symbol{}
		parent.Synopsis = strings.TrimSuffix(parent.Synopsis, "{ ... }")
		for _, c := range parent.Children {
			cm[c.Kind] = append(cm[c.Kind], c)
		}
		for _, syms := range cm {
			sortSymbolsGroup(syms)
		}
		symbols := append(append(append(
			cm[internal.SymbolKindField],
			cm[internal.SymbolKindConstant]...),
			cm[internal.SymbolKindVariable]...),
			cm[internal.SymbolKindFunction]...)
		if strings.Contains(parent.Synopsis, "interface") {
			parent.Children = append(cm[internal.SymbolKindMethod], symbols...)
		} else {
			parent.Children = append(symbols, cm[internal.SymbolKindMethod]...)
		}
	}
	for _, syms := range sm {
		sortSymbolsGroup(syms)
	}

	var out [][]*Symbol
	for _, section := range []internal.SymbolSection{
		internal.SymbolSectionConstants,
		internal.SymbolSectionVariables,
		internal.SymbolSectionFunctions,
		internal.SymbolSectionTypes} {
		if sm[section] != nil {
			out = append(out, sm[section])
		}
	}
	return out
}

func sortSymbolsGroup(syms []*Symbol) {
	sort.Slice(syms, func(i, j int) bool {
		return syms[i].Synopsis < syms[j].Synopsis
	})
}

// ParseVersionsDetails returns a map of versionToNameToUnitSymbol based on
// data from the proovided VersionDetails.
func ParseVersionsDetails(vd VersionsDetails) (map[string]map[string]*internal.UnitSymbol, error) {
	versionToNameToSymbol := map[string]map[string]*internal.UnitSymbol{}
	for _, vl := range vd.ThisModule {
		for _, vs := range vl.Versions {
			v := vs.Version
			versionToNameToSymbol[v] = map[string]*internal.UnitSymbol{}
			for _, syms := range vs.Symbols {
				for _, s := range syms {
					if s.New {
						versionToNameToSymbol[v][s.Name] = unitSymbol(s)
					}
					for _, c := range s.Children {
						versionToNameToSymbol[v][c.Name] = unitSymbol(c)
					}
				}
			}
		}
	}
	return versionToNameToSymbol, nil
}

// unitSymbol returns an *internal.unitSymbol from the provided *Symbol.
func unitSymbol(s *Symbol) *internal.UnitSymbol {
	us := &internal.UnitSymbol{
		SymbolMeta: internal.SymbolMeta{
			Name: s.Name,
		},
	}
	if len(s.Builds) == 0 {
		us.AddBuildContext(internal.BuildContextAll)
	}
	for _, b := range s.Builds {
		parts := strings.SplitN(b, "/", 2)
		var build internal.BuildContext
		switch parts[0] {
		case "linux":
			build = internal.BuildContextLinux
		case "darwin":
			build = internal.BuildContextDarwin
		case "windows":
			build = internal.BuildContextWindows
		case "js":
			build = internal.BuildContextJS
		}
		if us.SupportsBuild(build) {
			fmt.Printf("duplicate build context for %q: %v\n", s.Name, build)
		}
		us.AddBuildContext(build)
	}
	return us
}