package app

import (
	"fmt"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/stage"
)

// BoundedPlan is one validated inclusive range of the canonical pipeline.
// It owns effective endpoints and membership so command, runner, and
// composition callers do not independently interpret range bounds.
type BoundedPlan struct {
	stages          []stage.Stage
	canonicalNames  []string
	startIndex      int
	endIndex        int
	explicitFrom    bool
	explicitThrough bool
}

// BuildBoundedPlan selects an inclusive contiguous range of the canonical
// pipeline. Empty endpoints default to the beginning or end respectively.
func BuildBoundedPlan(from, through string) (BoundedPlan, error) {
	registry := stage.All()
	names := make([]string, len(registry))
	indices := make(map[string]int, len(registry))
	for index, candidate := range registry {
		if candidate == nil {
			return BoundedPlan{}, fmt.Errorf("build bounded plan: canonical stage %d is nil", index)
		}
		name := candidate.Name()
		if _, duplicate := indices[name]; duplicate {
			return BoundedPlan{}, fmt.Errorf("build bounded plan: duplicate canonical stage %q", name)
		}
		names[index] = name
		indices[name] = index
	}
	if len(registry) == 0 {
		return BoundedPlan{}, fmt.Errorf("build bounded plan: canonical stage registry is empty")
	}

	start := 0
	if from != "" {
		var ok bool
		start, ok = indices[from]
		if !ok {
			return BoundedPlan{}, fmt.Errorf("build bounded plan: unknown from stage %q; valid stages: %s", from, strings.Join(names, ", "))
		}
	}
	end := len(registry) - 1
	if through != "" {
		var ok bool
		end, ok = indices[through]
		if !ok {
			return BoundedPlan{}, fmt.Errorf("build bounded plan: unknown through stage %q; valid stages: %s", through, strings.Join(names, ", "))
		}
	}
	if start > end {
		return BoundedPlan{}, fmt.Errorf("build bounded plan: from stage %q occurs after through stage %q; valid stages: %s", from, through, strings.Join(names, ", "))
	}

	return BoundedPlan{
		stages:          append([]stage.Stage(nil), registry[start:end+1]...),
		canonicalNames:  append([]string(nil), names...),
		startIndex:      start,
		endIndex:        end,
		explicitFrom:    from != "",
		explicitThrough: through != "",
	}, nil
}

// Stages returns a copy of the selected canonical stages.
func (p BoundedPlan) Stages() []stage.Stage {
	return append([]stage.Stage(nil), p.stages...)
}

// Names returns selected stage names in canonical order.
func (p BoundedPlan) Names() []string {
	out := make([]string, 0, len(p.stages))
	for _, candidate := range p.stages {
		out = append(out, candidate.Name())
	}
	return out
}

// From returns the effective inclusive start stage.
func (p BoundedPlan) From() string {
	if len(p.canonicalNames) == 0 || p.startIndex < 0 || p.startIndex >= len(p.canonicalNames) {
		return ""
	}
	return p.canonicalNames[p.startIndex]
}

// Through returns the effective inclusive end stage.
func (p BoundedPlan) Through() string {
	if len(p.canonicalNames) == 0 || p.endIndex < 0 || p.endIndex >= len(p.canonicalNames) {
		return ""
	}
	return p.canonicalNames[p.endIndex]
}

// Contains reports whether a canonical stage is selected by the range.
func (p BoundedPlan) Contains(name string) bool {
	for _, candidate := range p.stages {
		if candidate.Name() == name {
			return true
		}
	}
	return false
}

// PrefixNames returns canonical stages excluded before the selected start.
func (p BoundedPlan) PrefixNames() []string {
	if p.startIndex <= 0 || p.startIndex > len(p.canonicalNames) {
		return nil
	}
	return append([]string(nil), p.canonicalNames[:p.startIndex]...)
}

// HasExplicitBounds reports whether either endpoint was supplied by the caller.
func (p BoundedPlan) HasExplicitBounds() bool {
	return p.explicitFrom || p.explicitThrough
}

// BuildFullPlan returns the canonical full stage list in deterministic order.
func BuildFullPlan() []stage.Stage {
	plan, err := BuildBoundedPlan("", "")
	if err != nil {
		panic(err)
	}
	return plan.Stages()
}

// BuildSingleStagePlan returns a one-stage plan for an exact stage name.
func BuildSingleStagePlan(name string) ([]stage.Stage, error) {
	s, err := stage.Select(name)
	if err != nil {
		return nil, fmt.Errorf("build stage plan: %w", err)
	}
	return []stage.Stage{s}, nil
}