package cli

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"strings"
)

// Context is a type that is passed through to
// each Handler action in a cli application. Context
// can be used to retrieve context-specific args and
// parsed command-line options.
type Context struct {
	context.Context
	App           *App
	Command       *Command
	shellComplete bool
	flagSet       *flag.FlagSet
	fromFlagSet   map[string]bool
	parentContext *Context
}

// NewContext creates a new context. For use in when invoking an App or Command action.
func NewContext(app *App, set *flag.FlagSet, parentCtx *Context) *Context {
	c := &Context{App: app, flagSet: set, parentContext: parentCtx}
	if parentCtx != nil {
		c.Context = parentCtx.Context
		c.shellComplete = parentCtx.shellComplete
		if parentCtx.flagSet == nil {
			parentCtx.flagSet = &flag.FlagSet{}
		}
	}

	// pre-compute flag seen on the command line at this context
	c.fromFlagSet = make(map[string]bool)
	if set != nil {
		set.Visit(func(f *flag.Flag) {
			c.fromFlagSet[f.Name] = true
		})
	}

	c.Command = &Command{}

	if c.Context == nil {
		c.Context = context.Background()
	}

	return c
}

// NumFlags returns the number of flags set
func (c *Context) NumFlags() int {
	return c.flagSet.NFlag()
}

// Set sets a context flag to a value.
func (c *Context) Set(name, value string) error {
	err := c.flagSet.Set(name, value)
	if err == nil {
		c.fromFlagSet[name] = true
	}

	return err
}

// IsSet determines if the flag was actually set
func (c *Context) IsSet(name string) bool {
	for ctx := c; ctx != nil; ctx = ctx.parentContext {
		// try flags parsed from command line first
		if ctx.flagSet.Lookup(name) == nil {
			// flag not defined in this context
			continue
		}
		if ctx.flagOnCommandLine(name) {
			return true
		}

		// now see if value was set externally via environment
		definedFlags := ctx.Command.Flags
		if ctx.Command.Name == "" && ctx.App != nil {
			definedFlags = ctx.App.Flags
		}
		for _, ff := range definedFlags {
			for _, fn := range ff.Names() {
				if fn == name {
					if ff.IsSet() {
						return true
					}
					break
				}
			}
		}
	}

	return false
}

func (c *Context) flagOnCommandLine(name string) bool {
	return c.fromFlagSet[name]
}

// LocalFlagNames returns a slice of flag names used in this context.
func (c *Context) LocalFlagNames() []string {
	var names []string
	c.flagSet.Visit(makeFlagNameVisitor(&names))
	return names
}

// FlagNames returns a slice of flag names used by the this context and all of
// its parent contexts.
func (c *Context) FlagNames() []string {
	var names []string
	for _, ctx := range c.Lineage() {
		ctx.flagSet.Visit(makeFlagNameVisitor(&names))
	}
	return names
}

// Lineage returns *this* context and all of its ancestor contexts in order from
// child to parent
func (c *Context) Lineage() []*Context {
	var lineage []*Context

	for cur := c; cur != nil; cur = cur.parentContext {
		lineage = append(lineage, cur)
	}

	return lineage
}

// Value returns the value of the flag corresponding to `name`
func (c *Context) Value(name string) interface{} {
	if fs := lookupFlagSet(name, c); fs != nil {
		return fs.Lookup(name).Value.(flag.Getter).Get()
	}
	return nil
}

// Args returns the command line arguments associated with the context.
func (c *Context) Args() Args {
	ret := args(c.flagSet.Args())
	return &ret
}

// NArg returns the number of the command line arguments.
func (c *Context) NArg() int {
	return c.Args().Len()
}

func lookupFlag(name string, ctx *Context) Flag {
	for _, c := range ctx.Lineage() {
		if c.Command == nil {
			continue
		}

		for _, f := range c.Command.Flags {
			for _, n := range f.Names() {
				if n == name {
					return f
				}
			}
		}
	}

	if ctx.App != nil {
		for _, f := range ctx.App.Flags {
			for _, n := range f.Names() {
				if n == name {
					return f
				}
			}
		}
	}

	return nil
}

func (c *Context) resolveFlagDeep(name string) *flag.Flag {
	var src *flag.Flag
	for cur := c; cur != nil; cur = cur.parentContext {
		if f := cur.flagSet.Lookup(name); f != nil {
			if cur.flagOnCommandLine(name) {
				// we've found most specific instance on command line, use it
				src = f
				break
			}
			if src == nil {
				// flag was defined, but value is not present among flags of the current context
				// remember the most specific instance of the flag not from command line as fallback
				src = f
			}
		}
	}
	return src
}

func lookupFlagSet(name string, ctx *Context) *flag.FlagSet {
	for _, c := range ctx.Lineage() {
		if f := c.flagSet.Lookup(name); f != nil {
			return c.flagSet
		}
	}

	return nil
}

func copyFlag(name string, ff *flag.Flag, set *flag.FlagSet) {
	switch ff.Value.(type) {
	case Serializer:
		_ = set.Set(name, ff.Value.(Serializer).Serialize())
	default:
		_ = set.Set(name, ff.Value.String())
	}
}

func normalizeFlags(flags []Flag, set *flag.FlagSet) error {
	visited := make(map[string]bool)
	set.Visit(func(f *flag.Flag) {
		visited[f.Name] = true
	})
	for _, f := range flags {
		parts := f.Names()
		if len(parts) == 1 {
			continue
		}
		var ff *flag.Flag
		for _, name := range parts {
			name = strings.Trim(name, " ")
			if visited[name] {
				if ff != nil {
					return errors.New("Cannot use two forms of the same flag: " + name + " " + ff.Name)
				}
				ff = set.Lookup(name)
			}
		}
		if ff == nil {
			continue
		}
		for _, name := range parts {
			name = strings.Trim(name, " ")
			if !visited[name] {
				copyFlag(name, ff, set)
			}
		}
	}
	return nil
}

func makeFlagNameVisitor(names *[]string) func(*flag.Flag) {
	return func(f *flag.Flag) {
		nameParts := strings.Split(f.Name, ",")
		name := strings.TrimSpace(nameParts[0])

		for _, part := range nameParts {
			part = strings.TrimSpace(part)
			if len(part) > len(name) {
				name = part
			}
		}

		if name != "" {
			*names = append(*names, name)
		}
	}
}

type requiredFlagsErr interface {
	error
	getMissingFlags() []string
}

type errRequiredFlags struct {
	missingFlags []string
}

func (e *errRequiredFlags) Error() string {
	numberOfMissingFlags := len(e.missingFlags)
	if numberOfMissingFlags == 1 {
		return fmt.Sprintf("Required flag %q not set", e.missingFlags[0])
	}
	joinedMissingFlags := strings.Join(e.missingFlags, ", ")
	return fmt.Sprintf("Required flags %q not set", joinedMissingFlags)
}

func (e *errRequiredFlags) getMissingFlags() []string {
	return e.missingFlags
}

func checkRequiredFlags(flags []Flag, context *Context) requiredFlagsErr {
	var missingFlags []string
	for _, f := range flags {
		if rf, ok := f.(RequiredFlag); ok && rf.IsRequired() {
			var flagPresent bool
			var flagName string

			for _, key := range f.Names() {
				if len(key) > 1 {
					flagName = key
				}

				if context.IsSet(strings.TrimSpace(key)) {
					flagPresent = true
				}
			}

			if !flagPresent && flagName != "" {
				missingFlags = append(missingFlags, flagName)
			}
		}
	}

	if len(missingFlags) != 0 {
		return &errRequiredFlags{missingFlags: missingFlags}
	}

	return nil
}