package alias

import (
	"errors"
	"reflect"
	"strconv"
	"strings"
	"testing"

	"gitea.maximumdirect.net/eric/CommandKit/internal/commandpath"
)

func TestResolverUsesLongestTokenPrefixAndPreservesSuffix(t *testing.T) {
	resolver, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"app", "collections"}},
	})
	if err != nil {
		t.Fatal(err)
	}

	got := resolver.Resolve(commandpath.Path{"list", "collections", "extra"})
	want := commandpath.Path{"app", "collections", "extra"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
	got = resolver.Resolve(commandpath.Path{"list", "prompts"})
	want = commandpath.Path{"promptkit", "list", "prompts"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
	reversed, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"app", "collections"}},
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
	})
	if err != nil {
		t.Fatal(err)
	}
	if got := reversed.Resolve(commandpath.Path{"list", "collections", "extra"}); !got.Equal(commandpath.Path{"app", "collections", "extra"}) {
		t.Fatalf("reverse-order Resolve() = %#v", got)
	}
}

func TestResolverFallsBackAfterLongerTokenMatchFails(t *testing.T) {
	resolver, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"a"}, Target: commandpath.Path{"short"}},
		{Source: commandpath.Path{"a", "b", "c"}, Target: commandpath.Path{"long"}},
	})
	if err != nil {
		t.Fatal(err)
	}
	got := resolver.Resolve(commandpath.Path{"a", "b", "x"})
	want := commandpath.Path{"short", "b", "x"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
}

func TestResolverDoesNotMatchUnknownTokens(t *testing.T) {
	resolver, err := NewResolver([]Mapping{{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}}})
	if err != nil {
		t.Fatal(err)
	}
	input := commandpath.Path{"listing", "collections"}
	got := resolver.Resolve(input)
	if !got.Equal(input) {
		t.Fatalf("Resolve() = %#v, want unchanged %#v", got, input)
	}
}

func TestCompiledMachineMatchesDirectResolver(t *testing.T) {
	mappings := []Mapping{
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"promptkit", "list", "collections"}},
		{Source: commandpath.Path{"pk"}, Target: commandpath.Path{"promptkit"}},
		{Source: commandpath.Path{"promptkit", "list", "bundles"}, Target: commandpath.Path{"promptkit", "list", "collections"}},
		{Source: commandpath.Path{"short"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"short", "b", "c"}, Target: commandpath.Path{"long"}},
	}
	resolver, machine, err := Compile(mappings)
	if err != nil {
		t.Fatal(err)
	}
	for key, operation := range machine.transitions {
		if len(operation.push) > 2 {
			t.Fatalf("transition %+v pushes %d symbols", key, len(operation.push))
		}
	}
	cases := []commandpath.Path{
		{"list"},
		{"list", "prompts"},
		{"list", "collections"},
		{"list", "collections", "extra"},
		{"pk", "list", "bundles", "tail"},
		{"short", "b", "x"},
		{"unknown", "operand"},
		{},
	}
	for _, marker := range []symbolKind{endSymbol, boundarySymbol} {
		for _, input := range cases {
			t.Run(input.String(), func(t *testing.T) {
				got, err := runMachineForTest(machine, input, marker)
				if err != nil {
					t.Fatal(err)
				}
				want := expectedSymbols(machine, resolver.Resolve(input), marker)
				if !reflect.DeepEqual(got, want) {
					t.Fatalf("machine result = %#v, want direct result %#v", got, want)
				}
			})
		}
	}
}

func TestResolverTreatsIdenticalMappingsAsIdempotent(t *testing.T) {
	mapping := Mapping{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}}
	resolver, err := NewResolver([]Mapping{mapping, mapping})
	if err != nil {
		t.Fatal(err)
	}
	got := resolver.Resolve(commandpath.Path{"list", "prompts"})
	if want := (commandpath.Path{"promptkit", "list", "prompts"}); !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
}

func TestResolverRejectsInvalidAndConflictingMappings(t *testing.T) {
	for name, mappings := range map[string][]Mapping{
		"empty source": {{Target: commandpath.Path{"target"}}},
		"empty target": {{Source: commandpath.Path{"source"}}},
		"conflicting target": {
			{Source: commandpath.Path{"source"}, Target: commandpath.Path{"first"}},
			{Source: commandpath.Path{"source"}, Target: commandpath.Path{"second"}},
		},
	} {
		t.Run(name, func(t *testing.T) {
			if _, err := NewResolver(mappings); err == nil {
				t.Fatal("NewResolver() succeeded")
			}
		})
	}
}

func TestTerminationRejectsCyclesAndGrowingPaths(t *testing.T) {
	for name, mappings := range map[string][]Mapping{
		"direct cycle": {
			{Source: commandpath.Path{"a"}, Target: commandpath.Path{"b"}},
			{Source: commandpath.Path{"b"}, Target: commandpath.Path{"a"}},
		},
		"growing path": {
			{Source: commandpath.Path{"a"}, Target: commandpath.Path{"b", "extra"}},
			{Source: commandpath.Path{"b"}, Target: commandpath.Path{"a"}},
		},
		"suffix-dependent cycle": {
			{Source: commandpath.Path{"a"}, Target: commandpath.Path{"b"}},
			{Source: commandpath.Path{"b"}, Target: commandpath.Path{"group"}},
			{Source: commandpath.Path{"b", "x"}, Target: commandpath.Path{"a", "x"}},
		},
	} {
		t.Run(name, func(t *testing.T) {
			err := ValidateTermination(mappings)
			var loop *NonTerminationError
			if !errors.As(err, &loop) {
				t.Fatalf("ValidateTermination() error = %v, want NonTerminationError", err)
			}
			if len(loop.Mappings) == 0 {
				t.Fatal("NonTerminationError has no participating mappings")
			}
			for _, mapping := range loop.Mappings {
				if !strings.Contains(err.Error(), mapping.Source.String()) {
					t.Fatalf("error %q omits participating source %q", err, mapping.Source.String())
				}
			}
			if name == "suffix-dependent cycle" {
				resolver, err := NewResolver(mappings)
				if err != nil {
					t.Fatal(err)
				}
				if got := resolver.Resolve(commandpath.Path{"a"}); !got.Equal(commandpath.Path{"group"}) {
					t.Fatalf("bare route resolves to %#v, want [group]", got)
				}
				first, _, matched := resolver.ResolveOnce(commandpath.Path{"a", "x"})
				second, _, matchedAgain := resolver.ResolveOnce(first)
				if !matched || !matchedAgain || !second.Equal(commandpath.Path{"a", "x"}) {
					t.Fatalf("suffix cycle is not demonstrated: first %#v, second %#v", first, second)
				}
			}
		})
	}
}

func TestTerminationAcceptsConsumingRepetition(t *testing.T) {
	mappings := []Mapping{
		{Source: commandpath.Path{"a"}, Target: commandpath.Path{"group"}},
		{Source: commandpath.Path{"group", "again"}, Target: commandpath.Path{"a"}},
	}
	if err := ValidateTermination(mappings); err != nil {
		t.Fatalf("ValidateTermination() = %v", err)
	}
	resolver, err := NewResolver(mappings)
	if err != nil {
		t.Fatal(err)
	}
	got := resolver.Resolve(commandpath.Path{"a", "again", "again"})
	if want := (commandpath.Path{"group"}); !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
}

func TestTerminationUsesLongestMatchBeforeFollowingShorterRule(t *testing.T) {
	mappings := []Mapping{
		{Source: commandpath.Path{"a"}, Target: commandpath.Path{"b", "x"}},
		{Source: commandpath.Path{"b"}, Target: commandpath.Path{"a"}},
		{Source: commandpath.Path{"b", "x"}, Target: commandpath.Path{"group"}},
	}
	if err := ValidateTermination(mappings); err != nil {
		t.Fatalf("ValidateTermination() = %v", err)
	}
	resolver, err := NewResolver(mappings)
	if err != nil {
		t.Fatal(err)
	}
	if got := resolver.Resolve(commandpath.Path{"a"}); !got.Equal(commandpath.Path{"group"}) {
		t.Fatalf("Resolve() = %#v, want [group]", got)
	}
}

func TestTerminationAcceptsLongChainsInAnyRegistrationOrder(t *testing.T) {
	const count = 80
	mappings := make([]Mapping, 0, count)
	for index := 0; index < count; index++ {
		source := commandpath.Path{fmtAliasName(index)}
		target := commandpath.Path{fmtAliasName(index + 1)}
		if index == count-1 {
			target = commandpath.Path{"canonical"}
		}
		mappings = append(mappings, Mapping{Source: source, Target: target})
	}
	if err := ValidateTermination(mappings); err != nil {
		t.Fatalf("forward registration order: %v", err)
	}
	for left, right := 0, len(mappings)-1; left < right; left, right = left+1, right-1 {
		mappings[left], mappings[right] = mappings[right], mappings[left]
	}
	if err := ValidateTermination(mappings); err != nil {
		t.Fatalf("reverse registration order: %v", err)
	}
}

func TestTerminalMarkersCannotBePopped(t *testing.T) {
	_, machine, err := Compile([]Mapping{{Source: commandpath.Path{"a"}, Target: commandpath.Path{"b"}}})
	if err != nil {
		t.Fatal(err)
	}
	pop := saturatePopSummaries(machine)
	for markerName, marker := range map[string]symbolKind{"end": endSymbol, "boundary": boundarySymbol} {
		for from := range pop {
			if from.symbol.kind == marker {
				t.Fatalf("%s marker can be popped from control %d", markerName, from.control)
			}
		}
	}
	if err := ValidateTermination(nil); err != nil {
		t.Fatalf("empty mapping set: %v", err)
	}
}

func fmtAliasName(index int) string {
	return "alias" + strconv.Itoa(index)
}

func expectedSymbols(machine *Machine, path commandpath.Path, marker symbolKind) []symbol {
	result := make([]symbol, 0, len(path)+1)
	for _, token := range path {
		result = append(result, machine.classify(token))
	}
	result = append(result, symbol{kind: marker})
	return result
}

func runMachineForTest(machine *Machine, input commandpath.Path, marker symbolKind) ([]symbol, error) {
	stack := expectedSymbols(machine, input, marker)
	control := machine.start
	for steps := 0; steps < 10000; steps++ {
		if control == machine.halt {
			return stack, nil
		}
		if len(stack) == 0 {
			return nil, errMachineStackEmpty
		}
		operation, ok := machine.transitions[transitionKey{control: control, read: stack[0]}]
		if !ok {
			return nil, errMachineTransitionMissing
		}
		stack = append(append([]symbol(nil), operation.push...), stack[1:]...)
		control = operation.next
	}
	return nil, errMachineTestDidNotHalt
}

var (
	errMachineStackEmpty        = testError("compiled machine emptied its stack")
	errMachineTransitionMissing = testError("compiled machine has no transition")
	errMachineTestDidNotHalt    = testError("compiled machine did not halt in the test interpreter")
)

type testError string

func (err testError) Error() string { return string(err) }

func (machine *Machine) classify(token string) symbol {
	if _, exists := machine.literals[token]; exists {
		return symbol{kind: literalSymbol, value: token}
	}
	return symbol{kind: otherSymbol}
}